package zheng;
import java.util.Scanner;
public class 兔子 {
	public static void main(String[] args) {
		Scanner a=new Scanner(System.in);
		System.out.println("输入月份");
		int s=a.nextInt();
		int s1=0,s2=1,s3=0,c=1;  //1.2月份兔子对数为1
		while(c<=s)
		{
		if(c==1||c==2)
		{
			if(c==1){
				s1=1;
			}else{
				s2=1;
			}
//			System.out.println(1);
			c++;
		}
		else{
			s3=s1+s2;
			s1=s2;
			s2=s3;
//			System.out.println(s3);
			c++;	
		}
		
		}
		System.out.println(s3);
	}
}		
			
		
	



